search slide
search slide
pages bottom

Researchers develop a new kind of blue ‘fire tornado’

Fire whirls are devastating, incompletely understood pyrodynamic events. They happen when a wildfire is so advanced that it makes its own wind. When building a campfire, if you’ve laid it well, you’ll often notice that the smoke and sparks make a lazy spiral as they rise. Fluid dynamics and fire science haven’t yet nailed down exactly what makes a plume of smoke rise in a spiral, but it’s easy to see that it often does. That phenomenon, writ large, is what makes fire whirls: the spiraling updraft above an out-of-control fire can fling burning debris through the air, fell trees, and even burn people alive.

Now, a group of researchers from the University of Maryland are bending the firenado to their own, more benevolent uses. This makes my inner pyromaniac intensely happy.

In much the same way as rocket stoves are physically arranged to control the currents of air through a combustive center, scientists figured out how to induce a fire whirl by just putting two quartz half-cylinders above their fire. What they produced was a pure, spiraling blue flame, smokeless and silent. They’ve named it a blue whirl. “A fire whirl is usually turbulent, but this blue whirl is very quiet and stable without visible or audible signs of turbulence,” said Huahua Xiao, coauthor.

“Blue whirls evolve from traditional yellow fire whirls. The yellow color is due to radiating soot particles, which form when there is not enough oxygen to burn the fuel completely,” said professor of engineering Elaine Oran, coauthor. “Blue in the whirl indicates there is enough oxygen for complete combustion, which means less or no soot, and is therefore a cleaner burn.”

These results represent a new way to control how fire does what it does, both by changing the vortex mode of the flame and by altering the behavior of the fuel. When the researchers tested out their technique over a scaled-down oil spill, the blue whirl made the whole oil slick start to rotate and draw inward toward the flame, sometimes removing any visible oil. After the vortex had exhausted its fuel, the researchers leaned down with a butane torch, but found that there was nothing left to burn.

Think about that: a stable, controlled vortex of flame that can burn crude oil completely, and exploits surface tension and viscosity to feed itself in lieu of a physical wick.

A cleaner burn is really important, for reasons that go beyond air quality in the lab. During oil spills like the 2010 Deepwater Horizon disaster, in-place burning is one tactic cleanup crews use to reduce the volume of the spill. But oil fires are so bad they’re almost unreal, because of the huge plumes of impenetrable, toxic black smoke, and in situ burning is no exception. The fact that it’s over water might even make it worse, because the waves move around all the toxic crap left when the oil burns. The blue whirl might be exactly the thing for oil spills: it burns hot, smokeless, and steady, even when it’s burning crude oil. And it draws up the oil as it burns.

The researchers are conscious of the need to see whether we can make the blue whirls stay lit over the open ocean, and they hope that publishing their technique can make fire more accessible to research. “A fire tornado has long been seen as this incredibly scary, destructive thing,” said fire protection engineer and coauthor Michael Gollner. “But, like electricity, can you harness it for good? If we can understand it, then maybe we can control and use it.”

You really should go read the original (and freely available!) paper, because these people articulate some fascinating things about how fire behaves.

Leave a Reply

Captcha image